docs: fix typos

[ycexiao]

What problem does this PR address

Closes#286

What should the reviewers do

Please see if the modifications are correct.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.10%. Comparing base (df988d7) to head (a25d800).
Report is 3 commits behind head on migration.

Additional details and impacted files

@@ Coverage Diff @@## migration #287 +/- ## ========================================== Coverage 95.10% 95.10% ========================================== Files 23 23 Lines 1123 1123 ========================================== Hits 1068 1068 Misses 55 55 

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[ycexiao]

@sbillinge, it's ready for review.